1. Field of the Invention
This invention relates to acrylates in which a large percentage of hydrogen atoms have been replaced by halogens and to polymers that include mer units derived from such halogenated acrylates.
2. Background of the Invention
Optically transparent polymers, especially those used for telecommunication applications, must have low absorptive loss in the infrared wavelengths, typically 1260-1360 nm and 1480-1580 nm. However, because these wavelengths are close to overtones of carbon-hydrogen bond vibration frequencies, minimization of the number of carbon-hydrogen bonds is desirable. While some organic compounds with few Cxe2x80x94H bonds are known, additional considerations of optical transparency, ease of polymerization, refractive index, chemical and mechanical stability, and the need to compete on a cost basis with glass prevent many such compounds from widespread use in polymeric optical devices.
U.S. Pat. Nos. 3,668,233, 3,981,928, and 4,010,212 describe acrylic acid esters (i.e., acrylates), prepared from esterification of acrylic acid with perfluorotertiary alkyl alcohols such as perfluoro-t-butyl alcohol, that can be used as inert heat exchange fluids and as homopolymeric water- and/or oil-repellent surface coatings.
European Patent Application No. 282,019 describes highly fluorinated, transparent acrylates specifically tailored for optical articles. These materials are prepared from cyclic or bicyclic alcohols containing few or no carbon-hydrogen bonds.
U.S. Pat. No. 3,544,535 describes the preparation and polymerization of 2-(pentafluorophenyl)hexafluoroisopropyl acrylate. Optical properties of the polymer are not described.
U.S. Pat. Nos. 3,520,863 and 3,723,507 describe a number of perfluorocycloalkyl acrylates and polymers thereof. Use of tertiary alcohols is not reported, and optical properties of the polymers are not discussed.
U.S. Pat. No. 5,045,397 describes the preparation and use of certain adhesives to be used in optical systems. A polymeric adhesive of a specified refractive index is prepared by copolymerization of specified monomers of known refractive indices. While some lightly fluorinated monomers are described, highly fluorinated monomers are not disclosed.
U.S. Pat. No. 5,223,593 describes acrylate monomers and their (co)polymers designed to have low Cxe2x80x94H bond density relative to poly(methylmethacrylate) so as to reduce vibrational band intensities in plastic optical fiber cores. Absorbance at 600-1200 nm was reduced, but absorbance at higher frequencies is not reported. The described acrylates were prepared from highly fluorinated primary alcohols.
U.S. Pat. No. 5,093,888 describes a polymeric optical device (specifically, an injection-molded Y-shaped splitter waveguide) that uses an amorphous polymeric adhesive that includes 2,2,2-trifluoroethyl methacrylate having a refractive index of 1.418 to hold optical fibers in a polytetrafluoro-ethylene spacer containing a fluorinated polyetheretherketone core.
U.S. Pat. No. 5,311,604 describes a method of manufacturing a polymeric optical interconnect. Useful polymers are said to be those transparent to the wavelength of light to be utilized. Listed examples include poly(methylmethacrylate) (xe2x80x9cPMMAxe2x80x9d), polycarbonates, polyurethanes, polystyrenes, and polyolefins. In one example, a xe2x80x9ccopolymer of deuterated PMMA-d8 (sic) and tetrafluoropropyl methacrylatexe2x80x9d is used to adhere optical fibers to a molded PMMA device.
U.S. Pat. No. 5,343,544 describes a polymeric optical interconnect. The device includes polymeric substrate and covering members that can be fabricated from, for example, a combination of fluorinated and non-fluorinated photopolymerizable (meth)acrylate and di(meth)acrylate monomers. The same combination of monomers is said to be useful for sealing optical fibers in the device. Substitution of fluorines for hydrogen atoms in the polymer is said to be capable of reducing the refractive index of the polymer and to reduce losses in near infrared wavelengths, but no example of a haloacrylate-only system and no indication of the degree to which loss or refractive index can be controlled are given. Copolymerization of two or more monomers is said to be able to provide a copolymer having a tailored refractive index.
Devices used in telecommunication applications (such as those described in ""604 and ""544, above) preferably meet certain standards for performance, durability, and the like. The standards most commonly referred to in discussing such devices are the so-called xe2x80x9cBellcore Specificationsxe2x80x9d. Requirements for fiber optic branching components include parameters for optical loss (i.e., loss that is in excess over that which is inherent in the device), useable wavelength ranges, resistance to performance variability caused by temperature and humidity, optical cross talk, water immersion, flammability, etc. All such parameters can depend, at least in part, on the materials used to make the device. For example, materials must have very low absorptive losses in the wavelength regions of 1260 to 1360 nm (nominally 1310 nm) and from 1480 to 1580 nm (nominally 1550 nm), over which ranges low losses must be maintained under extreme temperature and humidity conditions. For a 1xc3x972 splitter, the inherent loss is calculated to be 3.01 decibels (dB), where a decibel is defined as xe2x88x9210 log(Io/Ii) in which Io is the intensity of the output and Ii is the intensity of the input. Maximum allowable excess loss in a 1xc3x972 splitter is quantified as, e.g., no more than 0.25 dB per fiber plus no more than 0.5 dB per waveguide junction connecting an input fiber to an output fiber.
Presently available materials other than glass have not proven to be able to meet all, or even most, of these rigid requirements.
Briefly, the present invention provides halogenated acrylates having the general formula 
wherein
M is H, CH3, F, Cl, Br, I, or CF3; preferably M is H, F, or Cl; most preferably M is H because of availability, reactivity, and thermal stability;
A is oxygen or sulfur; and
Z can be a group having a maximum of 150 carbon atoms and can be 
in which each R1 independently is F, Cl, or Br; 
in which each R2 independently can be
(a) a perfluorinated, perchlorinated, or per(chlorofluoro)
(i) C1-C20 aliphatic group,
(ii) C3-C20 cycloaliphatic group,
(iii) C6-C20 aryl group,
(iv) C7-C20 aralkyl group, and
(v) C7-C20 alkaryl group,
(b) F, Cl, Br, I, Q (defined below), R4COOxe2x80x94, R4Oxe2x80x94, xe2x80x94COOR4, xe2x80x94OSO2R4, or xe2x80x94SO2OR4, wherein R4 is any group from (a)(i), (a)(ii), (a)(iii), (a)(iv), and (a)(v),
or any two adjacent R2 groups together can form a perfluorinated, perchlorinated, or per(chlorofluoro) cycloaliphatic or aromatic ring moiety in which n fluoro or chloro groups optionally can be replaced by R2 groups where n is a whole number in the range of 0 to 25, and R2 is as defined above, wherein Q is 
in which A is as defined as above, with the proviso that all R2 groups in the molecule can be the same only when R2 is not Cl, F, Br or I, and each R3 independently can be
(a) a perfluorinated, perchlorinated, or per(chlorofluoro)
(i) C1-C20 aliphatic group,
(ii) C3-C20 cycloaliphatic group,
(iii) C6-C20 aryl group,
(iv) C7-C20 aralkyl group, and
(v) C7-C20 alkaryl group,
(b) F, Cl, Br, I, Q (defined above), R4COOxe2x80x94, R4Oxe2x80x94, xe2x80x94COOR4, xe2x80x94OSO2R4, or
xe2x80x94SO2OR4, wherein R4 is any group from (a)(i), (a)(ii), (a)(iii), (a)(iv), and (a)(v),
or any two adjacent R3 groups together can form a perfluorinated, perchlorinated, or per(chlorofluoro) cycloaliphatic or aromatic ring moiety in which n fluoro or chloro groups optionally can be replaced by n R3 groups where n is a whole number in the range of 0 to 25, and R3 is as defined above;
(3) xe2x80x94C(Rf)2E in which
both Rf groups together can be part of a perfluorinated, perchlorinated, or per(chlorofluoro) cycloaliphatic ring group or each independently can be a perfluorinated, perchlorinated, or per(chlorofluoro)
(a) C1-C20 aliphatic groups,
(b) C3-C20 cycloaliphatic groups,
(c) C6-C20 aryl groups,
(d) C7-C20 aralkyl groups, or
(e) C7-C20 alkaryl groups,
(f) C4-C20 heteroaryl groups,
(g) C4-C20 heteroaralkyl groups,
(h) C4-C20 heteroalkaryl groups,
wherein the heteroatoms can be one or more of O, N, and S atoms, with the proviso that at least one Rf group includes one or more of the following:
(1) at least one straight-chain C4-C20 aliphatic or C4-C20 cycloaliphatic group,
(2) at least one ether oxygen atom, and
(3) at least one branched C3-C20 aliphatic group, and E can be Rf, 
wherein R1, R2, Rf, and Q are defined as above; or
(4) xe2x80x94CRf(E)2,
wherein each E independently is as defined above, and Rf is as defined above.
In another aspect, the present invention provides a polymer that includes at least one mer unit derived from the above-described haloacrylates as well as optical devices and optical materials made from such a polymer.
In yet another aspect, this invention provides di- and tri-functional acrylates as crosslinking agents with low hydrogen content, usually no more than the required three H atoms around each acrylate group.
In yet another aspect, this invention provides ether-containing perhalo-, preferably perfluoro- and perchlorofluoro ketones as intermediates to low H-content acrylates. Preferred compounds include 1,2-dichloroperfluoroethyl ether and 1,1,2-trichloroperfluoroethyl ether derivatives which can be prepared by the direct fluorination of a 1,1-dichloroethyl ether and 1,1,1-trichloroethyl ether, respectively.
In yet a further aspect, this invention provides 1,2-dichloroperfluoro/per(chlorofluoro) ethers useful in the synthesis of the above acrylates and also useful as precursors to perfluorovinyl ether monomers optionally substituted by functional groups. Preferred perfluorinated ketones have the structure R5fOCF2COCF3, R5fOCF2COCF2Cl, and R5fOCF2COCF2OR5f, wherein R5f is a linear perfluoroalkyl or perfluorooxyalkyl group having from two to twenty carbon atoms.
In this application, the following definitions apply unless a contrary intention is explicitly indicated:
(a) xe2x80x9cgroupxe2x80x9d or xe2x80x9ccompoundxe2x80x9d or xe2x80x9cmonomerxe2x80x9d or xe2x80x9cpolymerxe2x80x9d or xe2x80x9cmer unitxe2x80x9d means a chemical species that allows for substitution by conventional substituents that do not interfere with the desired product such as, for example, linear or branched alkyl or haloalkyl groups;
(b) xe2x80x9coptical couplerxe2x80x9d or xe2x80x9cinterconnectxe2x80x9d means a device that joins one or more input optical fibers to one or more output optical fibers and includes devices such as splitters and combiners;
(c) xe2x80x9cacrylatexe2x80x9d includes corresponding xe2x80x9cmethacrylatexe2x80x9d and other 2-substituted acrylates throughout this application; and
(d) subscript xe2x80x9cfxe2x80x9d refers to a perhalogenated group.
The halogenated acrylates of the present invention have relatively few Cxe2x80x94H bonds, usually no more than three (i.e., those around the acrylate unsaturation) or no more than five (around methacrylate unsaturation). This dearth of hydrogens means that these compounds have very little absorption in the infrared wavelengths of interest, i.e., 1260-1360 nm and 1480-1580 nm. Because these materials can be used in optical applications, particularly devices that guide light such as waveguides and optical interconnects, minimizing loss of signal due to absorption by the material of which the device is made is very important and desirable.
Despite the fact that the acrylates of the present invention are highly halogenated, they are relatively easy to polymerize, are optically clear, have low optical loss, are liquids or solids with relatively low melting points or dissolve sufficiently in lower-melting comonomers, provide amorphous polymers with good thermal stability and high molecular weights, and provide polymers (typically copolymers) having indices of refraction that effectively match those of glass optical fibers. These characteristics make them excellent candidates for use as materials in polymeric optical devices, especially waveguides and optical couplers.
Presently available optical devices made from glass are manufactured in one-at-a-time, handwork operations that are very labor intensive and prone to low productivity. Polymers of the invention can be processed automatically by known polymer processing methods into optical devices that are physically robust and are substantially identical, leading to significant improvements in product reliability and economics. Polymeric optical devices of the present invention can be mass produced and can be handled under severe field conditions without undue damage and/or loss of properties.